Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$90.68	10.297%	$100.0173	$100.02	$100.00	$100.00
Purchase #2	$5.95	9.687%	$6.5264	$6.53	$6.55	$6.50
Purchase #3	$160.33	3.709%	$166.2766	$166.28	$166.30	$166.30
Purchase #4	$92.84	4.818%	$97.313	$97.31	$97.30	$97.30
Purchase #5	$123.25	3.278%	$127.2901	$127.29	$127.30	$127.30
Purchase #6	$76.54	13.487%	$86.8629	$86.86	$86.85	$86.90
Purchase #7	$130.97	6.529%	$139.521	$139.52	$139.50	$139.50
7 purchase totals =	$680.56		$723.8073	$723.81	$723.80	$723.80